Vertebrates 2

Vertebrates 2 - Vertebrates 2: Mammals and human evolution...

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1 Vertebrates 2: Mammals and human evolution Mammalian Radiation in Wake of Cretaceous Extinctions With extinction of dinosaurs & fragmentation of continents at close of Mesozoic, mammals undergo extensive adaptive radiation ~ 5,300 extant species of mammals Derived characters of mammals Mammalia defined by presence of mammary glands – Milk, a balanced diet of fats, sugars, proteins, Mammals also have hair, made of the keratin – Hair & subcutaneous fat retain metabolic heat Mammals are warm blooded ( Endotherms) – supports active metabolism, made possible by Hyperactive Animals Active movement to catch prey and avoid predators fueled by ATP generated through aerobic respiration Tortoise may have won the race, but the hare and his kin dominate – Evolution of respiratory • Mitochondria in muscle & other active tissues • Closed circulatory system & ventral, chambered heart • Blood is oxygenated as it passes through capillaries in lungs Derived characters of mammals Born, not hatched – Fertilization internal, embryo develops in uterus – In eutherian (placental) mammals & marsupials lining of uterus & extraembryonic membranes form placenta , which nourishes embryo Generally, with larger brains than vertebrates of equivalent size – Many species capable of learning – Relatively long parental care extends time for learning important skills from parents – Unlike uniform conical teeth of most reptiles, mammalian Hearing Figure 34.31 Mammals evolved from synapsids in the late Triassic period Two bones that formerly made up the jaw joint were incorporated into the mammalian middle ear
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2 ANCESTRAL MAMMAL Monotremata Marsupialia Xenarthra Rodentia Lagomorpha Primates Dermoptera (flying lemurs) Scandentia (tree shrews) Carnivora Cetartiodactyla Perissodactyla Chiroptera Eulipotyphla Pholidota (pangolins) Proboscidea Sirenia Tubulidentata Hyracoidea Afrosoricida (golden moles and tenrecs) Macroscelidea (elephant shrews) Mammal phylogenetic tree Fig. 34-35a By the early Cretaceous, the three living lineages of mammals emerged: monotremes, marsupials, and eutherians Mammals did not undergo a significant adaptive radiation until after the Cretaceous Monotremes (meaning “single opening”) Monotremes are a small group of egg-laying mammals consisting of echidnas and the platypus Platypus No nipples! Low body temp No teeth in adults Short-beaked echidna Marsupials Marsupials include opossums, kangaroos, and koalas Higher metabolic rates, give birth to live young, have nipples The embryo develops within a placenta in the mother‟s uterus A marsupial is born very early in its development It completes its embryonic development while nursing in a maternal pouch called a marsupium Australian Marsupials Australian marsupials fill niches occupied by eutherian
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This note was uploaded on 03/22/2010 for the course BISC 120 taught by Professor Webb,wetzer,? during the Fall '07 term at USC.

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Vertebrates 2 - Vertebrates 2: Mammals and human evolution...

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